The zombie games each year are not necessarily consistent with each other. Out of the 5 (5?!) games so far, some have followed-up on the storyline of the previous game, and others have re-written the timeline completely, like making the outbreak recent and not 5-years ago when the first game was hosted.

Until a story is planned for the next game, nothing definite can really be answered about the world. Except that it's probably a modern times, IRL type world. No Zombie fighting in the middle-ages or in a fantasy forest is expected! Military, mercenaries, and scientists have been pretty consistent character types at the most recent games.

“No thief, however skillful, can rob one of knowledge, and that is why knowledge is the best and safest treasure to acquire.”